1. Field of the Invention
This invention relates to the steering control of rocket propelled vehicles by the use of thrust direction control or a combination of thrust direction control and steering fin control.
2. Description of the Related Art
As military aircraft become faster and more maneuverable, there is an increased need for faster and more maneuverable missiles with longer ranges to counter these threats. One method of increasing maneuverability of a missile is to use a steerable nozzle on the rocket motor to allow the direction of thrust to he controlled. This thrust vector control (TVC) affords greater maneuverability than traditional movable aerodynamic fins alone can provide under low speed or very high altitude where dynamic pressure is low.
The mechanism used to move the steerable nozzle is known as the nozzle actuator system. Such a system is disclosed in U.S. Pat. Nos. 5,505,408 of John M. Speicher, Allan A. Voigt and Che-Ram S. Voigt and 4,892,253 of John M. Speicher and Allan A. Voigt, both assigned to the same assignee as the instant application. The disclosures of those patents, incorporated herein by reference, are directed to a pair of orthogonal yoke plates used to actuate a rocket nozzle in accordance with steering commands of the missile control system. The yoke plates are coupled to the rocket nozzle, which is pivoted for movement at a ball-and-socket type joint, such that their translation in their prescribed planes moves the rocket nozzle to effect directional control of the rocket thrust.
A shortcoming of the prior art is that, although thrust direction control may provide adequate control of the missile along the yaw and pitch axes, motion along the roll axis must still be effected through the use of the missile aerofins. A problem arises at high altitudes, however, or under other such conditions of loss dynamic pressure, such as high angles of attack and low speeds, which significantly reduce the effectiveness of the aerofins. This reduces roll motion control and compromises the stability and maneuverability of the missile.
Attempts to obviate problems with reliance on aerofins for roll motion control have included the use of a plurality of rocket nozzles. Such a system is disclosed in U.S. Pat. Nos. 3,200,586 to Ernest. The need to independently control the rocket nozzles in such a system, however, detracts from its practicability by adding additional weight and cost and reducing the reliability of the rocket.
Other systems, such as those disclosed in U.S. Pat. No. 3,786,993 to Burgess et al. and U.S. Pat. No. 3,986,683 to Ellison, have used a single nozzle in conjunction with movable tabs disposed in the exhaust stream. However, in addition to increasing costs, these systems also introduce drag, which results in a host of attendant complications.
U.S. Pat. No. 3,200,587 to Tolson discloses still another system which provides attitude control of a rocket vehicle by shifting the nozzle transversely so that the thrust axis is no longer coincident with the central axis of the vehicle, thereby developing steering torque.
Another attempt to solve the problems of the prior art is disclosed in U.S. Pat. No. 5,662,290, application Ser. No. 08/679,849, of Che-Ram S. Voigt assigned to the same assignee as the instant invention, and incorporated herein by reference. The system of this patent employs a combination of missile fin control and directional nozzle control to effect motion in the yaw, pitch, and roll directions. The missile fin actuation mechanism is mechanically linked to the nozzle control mechanism, the nozzle control mechanism comprising of a pair of orthogonally-mounted yoke plates in which is mounted an interface yoke plate which operates to effect motion of a plurality of rocket nozzles controlled by pairs. The interface yoke plate, however, is an additional moving component which increases the complexity and weight of the nozzle actuation device and which occupies valuable space within the missile.